Dynamic Line Management (DLM) is a technique for improving the stability of DSL connections. It is particularly useful when operating DSL connections at close to their maximum speed, because under these conditions external noise affecting the transmitted signal can cause the transceivers to be unable to successfully recover the signal to be transmitted with sufficient reliability to enable the connection to be maintained. If this occurs, the connection needs to be re-established. This is referred to as a re-synch or a re-train and the user notices a temporary loss of service while the connection is re-established. Re-synchs are generally found to be particularly annoying by end users.
DLM seeks to minimize such re-synchs by automatically analysing DSL connections (especially the rate of occurrence of re-synchs) and varying certain parameters which can affect the likelihood of re-synchs occurring (for example the depth of interleaving, the amount of redundancy built into the encoding used, etc.). Typically, this is done by using a number of different profiles having various different sets of values for the parameters most likely to have an impact on the stability or otherwise of a DSL connection and moving a particular connection between different profiles until a profile is found which has an acceptable stability. The profiles are applied at the local exchange (sometimes referred to—especially in the USA—as the central office) usually within a piece of equipment known as a Digital Subscriber Line Access Multiplexer (DSLAM) which houses a number of DSL transceiver units as is well known in the art.
Typically, the profiles are conceptually able to be thought of as ranging between more aggressive and less aggressive, where the more aggressive profiles tend to provide better services to the user (especially in terms of higher bit rates and lower latencies) but are more likely to result in the line being unstable, whereas less aggressive profiles tend to offer lower bit rates and/or latencies but greater stabilities.
All of the DLM solutions known to the present applicant use, as at least one of the metrics used in monitoring the performance of a line, the number of re-trains or re-synchs occurring on a line within a predetermined period of time. However, the present inventors have realized that this metric can in certain circumstances be misleading and it should therefore be processed to provide a more reliable metric of line performance.